Wouldn't the transmitter have to accept a digital audio input in order to broadcast RDS? It seems to be analog only and I can't seem to get this to work.
Thanks for the info RF. Now if only I could figure out how to throw RDS in the audio chain. :-) It seems to be pretty complicated with the winamp version of stereo tool and Breakaway BP.
The Chinese do make some cool stuff, but these ELE transmitters seem to have cooling issues. I'm going to cut a square under the case to mount the output final to a heatsink. For now, a CPU fan does the trick.
I bought this transmitter off ebay at a discounted price and I can't figure out what these RDS "receivers" are supposed to do. They darn sure don't transmit RDS to a radio. I tried to contact the seller but they won't reply. Does anyone know about this?
I agree that attaching a heat sink and replacing the output resistor is the best way to go.
As a side note, I was playing around tonight and found that I was able to significantly increase the power of the transmitter by stretching the coils of wire (that go in front of the BNC output) outward.
Thanks I'll definately install the heat sink as you suggest, however do you know why this just started happening? The transmitter didn't do this when I first got it.
Plus I was able to keep it cool by taking off the top part of the case and putting a cpu fan on it. This prevented any part of it from heating up. But the sound was still very bad whereas before it was fantastic. Could something else be going on here?
Here's the problem, as soon as I turn on the transmitter, it seems to be ok. The longer I leave it on, the hotter it gets and the more the power output decreases. This is despite the rear fan working and low SWR with a dummy load or jpole antenna. I can set the SWR meter to forward and watch the needle drop.
Also, it doesn't sound as good anymore. Very weak, distorted and thin. Right before i noticed the problem I was testing the signal in my car and noticed a sharp decrease in volume.
Here are some pics of the circuit board. I'm an idiot with electronics but was wondering if someone could point me in the right direction to fixing it.
ELE EL-15H sounds excellent and has great output when it's working. But I have 2 units that have started to heat up during normal use and the power output decreases with the heat. I had to put a cpu fan on it to keep it cool, otherwise the power drops to nothing. Even with the fan it's not outputting 100% now. I believe this is because of some crudely designed circuit that allows you to decrease the RF output with the volume knob, but after some minimal use it begins to malfunction.
I have an HLLY 5watt unit that seems to be more solid, but it doesn't sound as good.
I had a 10 watt 50 ohm non-inductive resistor strapped to a heat sink and it appears to have burned itself out. For a long time it was hooked up to a 10 watt transmitter and working. The entire heat sink would get too hot to touch, but the transmitter remained cool and the SWR was 1.2. However, a few days ago it took a poop. The SWR shot up and the transmitter got hot.
Are these resistors not intended for long term use? Should I have used thermal grease or a fan?
Well it wasn't too bad. I used 3/4 copper pipe for stability and the process seemed to go smoothly. I was able to get the SWR down to 1.4, but that was with it sitting in my office in close proximity to electronics. I'm sure when I move it outside I'll get better results...
Thanks for your in depth explanation. Sounds like the j pole is the way to go. What makes it so finicky other than having to keep it away from metal ojbects? The youtube videos and tutorials I've seen online are specific about parts and lenghts. One video said to tune it by moving the wire clamps up and down the pipe.
I was planning to make a j pole antenna out of copper pipe, but since the ground plane seems to be pretty efficient when tuned properly I'm wondering if it's worth it. Do I remember correctly that someone said it offers more gain?
I acquired an SWR meter and on full power with a tuned ground plane I get 1.25. However, when I reduce the RF output the SWR sky rockets.
Another peculiar thing I noticed: When the transmitter has fully heated up from operating on reduced RF output, and when the RF power is turned back to maximum, the output power is reduced. As the transmitter begins to cool off (I put an ice pack on it), you can see the output power creep back up.
Odd. Even at 1mW to a ground plane 10 feet into the air should get you a couple of blocks. I know, I have a setup using the el-cheapo 1/4 ground plane on a 8 foot fence pole fed with the 1mW unit and surrounded by mobile homes, the signal reaches 3 blocks on a bad day, up to 5 on a good day after a rain. This is my "fall back" setup for those "don't feel right" days. I suspect you may have a VSWR issue. Even at 1mW a high VSWR will kill that flea signal just as bad as a high VSWR would kill a 1KW signal.
This doesn't get anywhere close to that. I tested it at the full 10 watt power and only got several miles if even that. I downloaded a program to calculate the lenghts of the ground plane and tuned it to my frequencey. Of course, I can't properly test it because i don't have anything to measure the SWR.
rfburns said:
How are you tapping the power after the attenuator, and is the attenuator a "non-inductive" load? The transmitter should operate at normal temperature even running through an attenuator, it is the attenuator that should be getting a bit warm. However with an attenuator inline or not, if there is a high VSWR on the feedline and/or antenna itself, no doubt that will make the TX run hot.
I believe the attenuator is non-inductive. If I run on full power with the attenuator the transmitter doesn't get hot at all, but the attenuator will burn your fingurs if you touch it. Whether it's a dummy load, ground plane or attenuator with ground plane the transmitter doesn't get hot unless the power is scaled back.
If the load, dummy or antenna, is a non-inductive 50 ohm load, or a well tuned antenna, the unit should run fine and sound good. A high VSWR will not only kill the signal coverage, but will also dampen the carrier bandwidth as well as shunt the channel separation by feeding all that back into the transmitter output, then into the driver stages and into the modulator and stereo generation circuits...be it a package IC or separate circuits.
Imagine if we could hear VSWR, much like how we can hear feedback from a microphone too close to a loudspeaker. What happens to sound when feedback is present? It gets "shunted" and overtaken by the feedback. Same happens to RF with a high VSWR and the audio also becomes overtaken by the VSWR, causing it to sound muddy or weak, along with a sweating transmitter getting too hot.
As OER suggested, get a SWR meter and check things. The Workman SWR -3P is a good meter and can be found in abundance on ebay for around 25 mulas.
The finals in those Chinese units have internal thermal and short protection, though the short protection is "short" lived, meaning too long of a short or high VSWR will blow out the final. Too bad they did not incorporate an auto-shut down or crowbar circuit to dampen the power level in the event of a high VSWR. Many operators believe that they can overcome a VSWR issue by simply cranking up the power to compensate, but all that increased RF power is doing nothing but increasing the VSWR ratio, and in turn dumping the increased reflected RF back into the output....POOF! (who let the smoke out...POOF...POOF POOF POOF!)
An improper matched antenna and coax can also cause increased spectrum garbage which will rob your transmitter of power output and scatter that power across the spectrum at the harmonic points.
With a proper match, you can crank up the power and the VSWR ratio should be the same, plus or minus a point or two in proportion to the power output. In any case, when properly tuned, the antenna and coax should present a near perfect load match. Taking the time to obtain that "as close as possible" match is well worth the effort in both signal coverage and sound quality.
Peace!
Thanks for the recommendation on the Workman SWR -3P. I will buy one.
When the ground plane is connected the sound is amazing. Fantastic stereo seperation and quite loud. It rivals that of one of the best sounding radio stations around here. I just had to tweak my audio processing to work with this unit. I tested it on a crappy car radio with crap speakers, so any inperfections stand out like a sore thumb.
Those Chinese units have a thermal protection built into them that actually works (ask me how I know) and I never lost an output transistor to heat. I did zap a couple because of bad mismatches with antennas.
How hot did yours get? I've not pointed my infrared thermometer at the case when it was running, but my 20 Watter is pretty cool to the touch with the fan running while broadcasting, although the heat sink inside is hot enough to burn you and my 1mW unit is cool as a cucumber when running and it isn't fan cooled.
I'd be checking the SWR and see what's going on.
Strangely enough I broadcasted into a wire wound resistor dummy load with an HLLY 5 watt for years (I was told this was like transmitting into open ended coax). The transmitter never burned up.
They actually sent me another unit by mistake, which arrived today. So I guess if burn this one up I have another one.
The heat is only an issue when the power is scaled back. Otherwise it remains cool.